Rail, Maritime and Transport union leader Bob Crow has died, it was reported today.

Mr Crow became the RMT union leader in 2002, and since then them RMT's membership increased from 57,000 to more than 80,000.

He died in the early hours of this morning after a heart attack, and news of his death caused a social media storm.

Former Mayor of London Ken Livingstone said: "I assumed he would be at my funeral not me at his.

"He fought really hard for his members. The only working-class people who still have well-paid jobs in London are his members.

"With the passage of time people will come to see that people like Bob Crow did a very good job."

Trade Union Congress general secretary Frances O'Grady said: "This is shocking news. Bob was an outstanding trade unionist, who tirelessly fought for his members, his industry and the wider trade union movement.

"He was always a good friend and comrade to me. We will miss him, and our thoughts are with his family and the RMT at this difficult time."

The union boss recently rose to national prominence over the London Underground tube strikes, when he became involved in a dispute over the planned closure of ticket offices with Mayor of London Boris Johnson.

The first London Underground strike closed the capital down in large parts, while the second strike was called off after striking a provisional agreement with Mr Johnson.

John McDonnell MP, the chair of the RMT Parliamentary Group, has told LBC: "Whatever you thought of him, he worked hard for his members. No one can doubt his dedication."

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In a statement on its website, RMT said: "It is with the deepest regret that RMT has to confirm that our General Secretary Bob Crow sadly passed away in the early hours of this morning.

"RMT would request that all media respect the privacy of the friends and family of Bob Crow at this distressing time."

London Assembly members now hope that a charter guaranteeing minimum levels of service for the Tube could be a way of halting ticket office closures.